The gasification of solid carbonaceous materials such as coal and coke is well known in the art. From a broad consideration, a combustible mixture of the carbonaceous fuel, together with a combustion supporting gas, is burned to produce a usable synthetic gas as well as a residual ash or solid material.
In a typical prior art apparatus for achieving a gasification process, the gasifier or reactor vessel is normally comprised of a heavy steel shell. Since the gasification process is carried out at an elevated temperature within the range of 1800.degree. to 3500.degree. F., and pressure about 5-250 atmospheres, at least a portion of the shell is insulated with a refractory material along the shell's inner walls.
The shell is generally disposed in an upright position, defining at the upper end a combustion chamber within which the carbonaceous fuel mixture is burned.
A burner positioned in the gasifier wall is communicated with a source of the carbonaceous fuel preferably in slurry form. It is communicated as well as with a source of a pressurized combustion supporting gas such as oxygen or air. In the burner, the solid and gaseous components are directed under pressure, from the burner discharge port, into the reactor combustion chamber.
In said combustion chamber, complete or partial combustion of the fuel results in the production of the synthetic gas, together as noted, with a solid residue. The latter normally takes the form of an ash, or solid particles which are initially whirled violently about the combustion chamber.
The lower end of the combustion chamber terminates at the chamber floor. The latter includes an opening through which the produced gas and the solid residue are conducted into a liquid holding quench chamber.
FIG. 1, illustrates a segment of a gasifier structure utilized in the prior art. To facilitate handling of the hot produced gas and residue, the quench chamber is disposed in the lower part of the reactor shell. Said quench chamber includes a pool of liquid coolant, preferably water, together with a dip tube which functions to conduct and guide the gas and solid materials into the water bath. The gas then emerges from the bath in cooled form.
The quench chamber is further provided with one or more discharge conductors for the produced gas. The lower end of said chamber includes an outlet means for removing the cooled, solid component in the form of a slurry by way of a lockhopper or similar apparatus.
A number of carbonaceous fuels are considered appropriate to the gasification process. These include coal, both anthracite and bituminous, as well as lignite, coke and other carbonaceous materials. It can be appreciated that each form of fuel is characterized by a particular composition and consequently results in a different form of produced gas as well as residual.
After any run of the reactor during which the synthetic gas is produced, the residuals will normally be at a temperature which exceeds their melting points. They will consequently flow downwardly along the wall of the gasifier to the floor of the combustion chamber.
From the latter, these fluidized solid materials will continue downwardly through the connecting segment between the gasifier combustion chamber, and the quench chamber. Both solids and gas will then pass into and through the liquid bath.
When it becomes necessary to shut down or discontinue operation of a gasifier run, the inflow of fuel mixture from the burner is discontinued such that the combustion event ceases. As the unit progressively cools, at least some of the residual materials, remaining on the reactor walls, will freeze and solidify.
Thereafter, when the unit is again activated for a subsequent run, it will normally be preheated prior to introduction of the gas producing fuel mixture. Preheating is generally achieved through use of a special burner in which the combustible mixture is burned to bring the combustion chamber temperature to a working level. When said level is reached, the preheat burner will be replaced by a fuel feeding burner. Thus, the combustible carbonaceous fuel is introduced into the hot combustion chamber and ignited.
It has been experienced that during the required preheat period within a temperature range of about 1400.degree. F. to 2200.degree. F., which precedes reactor start-up, certain of the solid deposits from the previous run, and particularly those which are rich in vanadium, will tend to oxidize. This phenomena is noticeably true when the previous fuel was comprised primarily of a petroleum coke. The formation of pentavalent vanadium for example, will create a molten material that flows down the combustion chamber walls and into the constricted throat at the combustion chamber lower end.
Due to the low flow of gases through the constricted throat under preheating conditions, and further due to the loss of radiant energy in the quench zone below the throat, the latter will remain relatively cool. This condition persists even though the gasifier combustion chamber may achieve temperatures within the range of 2000.degree. to 2200.degree. F.
As a result, the liquefied or flowing, vanadium rich slag will tend to deposit and then solidify onto the colder wall portions of the throat. If this freezing action persists, the solid material will progressively accumulate, and thereby create at least a partial barrier to passage of produced gas and ash from the combustion chamber.
During a reactor start-up period, even though temperature in the reactor constricted throat may rise due to the much higher flow rate of the hot gases, the switch to a reducing atmosphere within the reactor effectuates a change in the chemical character of the vanadium rich deposits.
The melting point of the deposited metal thus rises beyond the temperature of the produced gas. As a result, the deposits will remain in solid form within the reactor throat in spite of temperatures well above 2000.degree. F. This progressive development of a plugging or a blockage in the throat area creates excessive backpressures across the throat as the gas flow rate increases.
Toward overcoming this undesirable accumulation of material, or the forming of a barrier in the gasifier throat, which could eventually result in a complete or partial blockage, means is herein disclosed for gaseous flow to the throat area. The desired result is to maintain the throat and its adjacent radiant section clear of such deposits.
In a preferred embodiment, the gasifier throat, and its downstream radiant section are provided with at least one, and preferably with a plurality of high pressure fluid stream nozzles. The latter are positioned to open or discharge into the throat downstream, and are communicated either individually or through manifolding to a pressurized fluid source. The fluid, preferably hot gas, is formed as it leaves the fluid stream nozzles into high velocity streams, or a jet flow pattern suitable for dislodging solids from the throat and downstream walls.
The supplementary fluid is preferably a gas which is preheated. Further, the gas can be hot produced or synthetic gas which is recycled from the gas generator.
It is therefore an object of the invention to provide a gasifier for producing a synthetic gas wherein the gasifier throat is provided with means for maintaining the walls of the throat in a relatively free and uncluttered with solid matter.
A further object of the invention is to provide means in a gasifier unit for avoiding accumulation of solid residual particles in a gasifier's relatively constricted throat.
A still further objective is to maintain the efficiency of a gasifier unit from the point of view of producing a synthetic usable gas, by maintaining the gasifier throat in a relatively cleared condition.